Prince Kūhiō Day is an official holiday in the American state of Hawaii celebrated annually on March 26. It is dedicated to Prince Jonah Kūhiō Kalanianaʻole, who was heir to the throne of the Kingdom of Hawaii, and later served as territorial delegate in the U. S. Congress.

Prince Jonah Kūhiō Kalanianaʻole was born on March 26, 1871. He was a descendant of Kaumualii, the last independent supreme ruler of Kaua’i and Ni’ihau. After the death of his parents, he was adopted by his maternal aunt Kapi’olani, Queen Consort of the Kingdom of Hawaii. When the House of Kalākaua ascended to the throne, Prince Kūhiō became an heir.

In 1893, the Kingdom of Hawaii was overthrown, and the revolutionaries established the Republic of Hawaii. Kūhiō participated in a rebellion against the republic, was arrested and sentenced to a year in prison. Following the annexation of Hawaii by the United States, he left the country and traveled to Europe and then to Africa.

Kūhiō returned to Hawaii in 1902 to participate in politics. At first he joined the Home Rule Party of Hawaii, but then split from it and joined the Republican Party. In 1903, he was nominated as their candidate for Congress and was elected. Kūhiō represented the Territory of Hawaii in the Congress until his death in 1922.

Prince Kūhiō Day was officially established by the legislature of Hawaii in 1949. It is one of the only two holidays in the USA dedicated to royalty, the other being Kamehameha Day (June 11).